Low-power or high-speed data transmission may involve transmitters with Source-Series-Terminated (“SST”) or Voltage Mode Line (“VML”) drivers. Even though the following description is in terms of SST drivers, such description is likewise applicable to VML drivers and the like.
Signal swing or return loss performance of SST and SST-like devices depends in part on matching transmission impedance. By way of example and not limitation, field effect transistor (“FET”) device sizes and linear internal transistors may have to match impedance of external resistors, such as 100 ohms for differential and 50 ohms for single ended termination. Unfortunately, process-voltage-temperature (“PVT”) variation may render such impedance matching problematic.
Accordingly, it is desirable and useful to provide impedance tuning for source termination that is adaptable to PVT.